Some 21,000 succulents call the roof of New York City's Con Edison's three-story Learning Center in Long Island City, Queens. The facility - some pales in comparison to the 2.5 living roof atop the Postal service facility in mid-town Manhattan. Meanwhile Chicago, the city that plays host to more green roofs than any other US City, added some 600,000 square feet of green roofs last year bringing their total coverage to a whopping 7 million square feet according to a December Yale Environment 360 article. The city of Toronto even went so far as to mandate that new buildings above a certain size will have to cover at least 60% of their roofs with vegetation.

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Green roofs - roofs that are covered with vegetation -are hot, and for good reason.

According to research conducted by Con Edison and Columbia University on Con Edison's Long Island City green roof, the average winter heat loss was some 34% lower under the green roof than under the black roof, while the summer heat gain was 84% lower on the green roof than under the black roof.

In other words - green roofs keep buildings warmer in winter, reducing the need for heat, and cooler in summer, reducing the need for air conditioning.

That's a cost savings that over the 25-50 year life span of a roof will bring considerable cost savings, even including the increased cost of building a green roof.